The present application relates generally to the extraction of sweet compounds from Stevia leaves and debitterizing the same.
Extraction of components of value from plant material, e.g., plant leaves for food and pharmaceuticals, is widely practiced. Most of these processes use extraction by hot water and/or organic solvents for isolation of a particular compound or refining a class of compounds from the complex mixture. The stevia plant, stevia rebaudiana, contains sweetening compounds, such as glycosides, which are explained by Kinghom and Soejarto, 1985, as including Stevioside, rebaudioside A(RA), rebaudioside B(RB), rebaudioside C(RC), dulcosides A and dulcosides B.
The stevia plant also contains non-sweetening constituents, and selectively extracting the sweetening compounds from the non-sweetening constituents has been the subject of numerous studies over the past several decades. There have been several studies describing the extraction and purification of sweeteners from the dried leaves of the stevia plant (Adduci et al., 1987; Yokohama and Sugiyama, 1990; Liu et al., 1991). These conventional methods use large amounts of organic solvents and chemicals for refining natural source sweeteners. Also, U.S. Pat. No. 4,892,938 to Giovanetto discloses a rather complicated process that utilizes several unit operations, including water extraction at room temperature to 65° C., a first strongly acidic ion exchange, followed by a second weakly basic ion exchange for refining Stevioside.
Chinese Patent No. 1132840C discloses a method for purifying stevia glycosides through solid-liquid separation. In this process, stevia glycosides and ethanol are mixed at a ratio of 1:1.4-1.7 and dissolved with stirring. The resulting solution is subjected to solid-liquid separation, the solids and liquid obtained from which are decolorized and then dried to obtain purified stevia glycosides. The content of rebaudioside in the stevia product obtained from this process is 88%, and the product still contains undesirable aftertaste and high levels of impurities.
Chinese Patent No. 1098860C discloses a process for separating enriched stevia glycosides through vacuum filtration and ion exchange resin. The process uses a crude stevia glycosides source material with a ratio of Rebaudioside A to Stevioside ranging from 0.5 to 1.1. The crude stevia glycoside is dissolved by stirring the crude with an ethanol-water solvent. The mixture is then filtered to obtain a filtrate, after which the filtrate is desalinated with ion exchange resin and decolorized.
A useful discussion of related technology is found in A. I Bakal & L. O'Brien Nabors, “Stevioside” in Alternative Sweeteners, Marcel Decker Inc., N.Y. 1986 pp-295-307.
U.S. Pat. No. 5,112,610 discloses a method of making a natural sweetener based on Stevia rebaudiana that includes the extraction of plant parts of Stevia rebaudiana with a solvent to provide an extract, and subjecting the extract to an extraction with a supercritical gas to obtain an extraction residue which is freed from undesired and taste-impairing constituents. However, extraction with only a solvent is an expensive method, and the large amount of solvent has to be removed and disposed of may leave some residue. Moreover, extraction with supercritical gas may induce mixed test in the final product.
At present, there are five major methods being used in attempts to improve the taste of stevioside, which in its unmodified state leaves a bitter and unpleasant aftertaste. The first method is organic solvent distillation such as with the use of a medical alcohol as a solvent to increase the quality of the taste. However, since alcohol is used in the process, any residual alcohol may pose issues for the human body. Moreover, the production yield is low, which highly increases the production cost even though the unpleasant aftertaste persists.
The second method involves using resin to improve the quality of the taste of Stevioside, and involves washing the resin with acid and alkaline solution. The resin will attach to the stevioside in the production process, which leads to relative low yield. Again, the unpleasant aftertaste problem remains unsolved.
The third method involves adding an amino acid group to the stevioside to improve the taste. However, since a large quantity of amino acid is required in the production process, the end product has a relatively high caloric value, thus destroying one of the key benefits of using stevioside (i.e., as a low calorie sweetening agent). One additional issue of this method is that the cost of the added amino acids is relatively high, which in turn increases the production cost.
The forth method involves combining stevioside with glucose, sucrose, and/or lactose to create a stevioside/sugar mixture in an attempt to “mask” or “cover” the taste of the end product. One obvious disadvantage of such a method is that the addition of sugars to the mixture eliminates some of the benefits of using stevioside (e.g., as a low-calorie sweetener). Even with this mixture, however, the bitter taste of the stevioside compounds persists even though it may be partially masked by the presence of the sugars.
The fifth method is described, for example, in U.S. Pat. No. 4,219,571, which discloses a process for producing a sweetener that involves allowing glucosyl transferase to react with stevioside in an aqueous solution to transform the stevioside into an alpha-glycosyl stevioside and hence improve the quality of taste of stevioside by altering the structure of stevioside. It is unclear as to whether such a process actually results in a definitive improvement in the taste of the end product.
Thus, there remains a need for new processes of extracting and debitterizing stevia in a simplified and enhanced manner. Furthermore, there remains a need for a stevia extract that has no or low aftertaste, and a stevia extract that has less non-sweetening constituents.